1. Field
Embodiments of the present invention relate to an organic light emitting diode (OLED) display.
2. Description of the Related Art
A display device is used as a display for mobile information terminals such as a personal computer, a mobile phone, a personal digital assistant (PDA), and the like, or as a monitor of various information devices, and a liquid crystal display (LCD) using a liquid crystal panel, an organic light emitting diode (OLED) display device using organic light emitting elements, a plasma display panel (PDP), and the like, are widely known as the display device. Among them, an OLED display having excellent luminous efficiency, luminance, and viewing angle as well as a fast response speed has been the subject of much attention.
In the OLED display, a plurality of pixels are disposed in a matrix form on a substrate so as to be used as a display area, scan lines and data lines are connected to the pixels, and data signals are selectively applied to the pixels to display an image.
Such display devices can be categorized as a passive matrix light emitting display device or an active matrix light emitting display device depending on how pixels are driven. The passive matrix OLED display forms an anode to cross a cathode and selects a line to drive it.
The active matrix OLED display maintains a data signal, which is switched by a switching transistor, by using a capacitor, and applies the same to a driving transistor to control a current that flows to the OLED.
However, in the case of the active matrix OLED display, temperature change and/or pixel degradation may change the characteristics of the respective driving transistors, such as a threshold voltage (Vt) and/or charge mobility.
As a result of this change, even when the same data signal is applied to the driving transistors of the display pixels, there may be a difference between currents flowing to the respective OLEDs. As a result, each pixel may emit light with a different luminance.
In general, a driving current (I) flowing to the driving transistor and a driving voltage (V) corresponding to the data signal are related according to Equation 1.I=k×(V−Vt)p  Equation 1
Here, k is a variable relating to the mobility characteristic of the driving transistor, Vt is a variable relating to the threshold voltage characteristic, and p is a constant with a value of 1 to 2. Thus, for example, the mobility characteristic and the threshold voltage characteristic of the driving transistor can be acquired by using the relationship between the driving voltage (V) and the driving current (I).
As an example, when currents I1 and I2 flowing to the driving transistor for at least two voltage levels V1 and V2, respectively, of the driving voltage (V) are measured and substituted into Equation 1, two equations are calculated. When variables k and Vt are acquired from two concurrent equations and are then used to compensate the data signal, a luminance difference among pixels can be reduced.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.